Method of fibrillation



Sept. 17, 1968 P. 1.. SPIVY METHOD OF FIBRILLATION Filed Jan. 16. 1967 INVENTOR. P L. SPIVY ATTbR/VEVS United States Patent 3,401,517 METHOD OF FIBRILLATION Paul L. Spivy, Bartlesville, 0kla., assignor to Phillips Petroleum Company, a corporation of Delaware Filed Jan. 16, 1967, Ser. No. 609,427 Claims. (Cl. 57-157) ABSTRACT OF THE DISCLOSURE A method of forming a twisted fibrillation product comprising twisting a plastic film, passing same between a pair of rotating rolls, oscillating said rolls transversely to fibrillate said twisted film.

This invention relates to a method of fibrillating a fibrillatable film.

Heretofore when making cordage such as tying twine and baler twine from a fibrillatable material, the molecularly oriented fil-m was fibrillated while in the normally fiat state. Thereafter, the fibrillated film was twisted to form the familiar twine configuration. After the fibrillation step and the twisting step, the twisted fibrillated product was wound onto a roll and the roll inserted into an oven and heated at elevated temperatures for a time sufficient to effect some degree of permanent set in the twisted fibrillated film so that the film would not tend to unwind into a fiat configuration when removed from the roll for use.

It has now been found that the separate, expensive, and time consuming heating step can be eliminated without eliminating the function of that step by twisting the molecularly oriented film before it is fibrillated and then fibrillating the twisted film by passing same one or more times between at least one pair of rollers, at least one of which rollers is oscillating substantially parallel to its longitudinal axis and substantially perpendicular to the longitudinal axis of the twisted film. The rubbing action of the twisted film between the rollers not only causes fibrillation of the film but also affects a degree of permanency of the twist in the film that is substantially the same as that degree of permanency obtained by separately heating twisted fibrillated film in an oven as discussed hereinabove.

Accordingly, it is an object of this invention to provide a new and improved method for making a twisted, fibrillated product. It is another object of this invention to provide a new and improved method for making cordage such as tying twine or baling twine using a fibrillated film.

The utility of this invention is obvious in that the products produced by the method of this invention are useable as conventional cordage for tying objects together, tying boxes, packages, and the like closed, and other similarly obvious utilities.

By this invention fibrillatable films are films that have been molecularly oriented so that they can be broken up into separate, continuous filaments or into a unitary, integral network of longitudinally extending stern fibers integrally joined to one another at random points along the length thereof by a plurality of shorter, smaller diameter cross fibers. By molecular orientation or orientation, what is generally meant to be covered is deforming, e.g. stretching, the film at a temperature below that at which the film is substantially in the molten state to thereby plasticly elongate the film and increase the strength of the film at least in the direction in which it is elongated. Molecular orientation and fibrillation of plastic films is well known in the art. As an example, reference is made to U.S. Patent 3,003,304, the disclosure of which is hereby incorporated herein by reference.

In the drawing there is shown a system embodying this invention.

More specifically, there is shown in the drawing a roll of molecularly oriented film 1 fixed to shaft 2 which is rotated by motor 4 in a counterclockwise direction as shown by arrow 3. Carried about or slightly above roll 1 is ring member 5 which in turn carries free sliding C guide 6. Guide 6 is free to slide in any direction around the entire inner periphery of ring 5. Eyelet 7 is spaced from ring 5 so as to guide twisted film 8 into the nip of contiguous rolls 9 and 10.

In the particular embodiment of the drawing, bottom roll 10 is an idle roll while upper roll 9 is oscillated in the direction of double-headed arrow 11 which direction is substantially parallel to the longitudinal axes of rolls 9 and 10 and in a plane substantially perpendicular to the longitudinal axis of twisted film 8. Roller 9 is oscillated in a conventional manner by apparatus (not shown) which will be obvious to one skilled in the art, e.g. an automatically reversible hydraulic piston. The oscillating action of roll 9 against twisted film 8 which is pressed between rolls 9 and 10 causes fibrillation of that twisted film and at the same time imparts a degree of permanency of twist to that twisted film. After issuing from between rolls 9 and 10, the twisted, fibrillated product can be taken up on roll 12 for storage, sale, or subsequent disposition as desired.

In the method of this invention the twisted film 8 can be pased between rolls 9 and 10 more than one time depending on the degree of fibrillation desired. For example, the twisted, fibrillated film issuing from between rolls 9 and 10 for the first time can be recycled to the upstream side of rolls 9 and 10 and again inserted into the nip of those rolls so that the same film is passed between the same pair of rolls two times. 'Of course, the same film can be recycled betweenthe same pair of rolls as many times as desired, e.g. four, five, six, or more times. Also, more than one set of oscillating rolls can be employed if desired. Further, three rolls in a pressing engagement similar to that shown in the drawing can be employed so the twisted film to be fibrillated can be passed between the two inner faces formed by the three rollers one or more times depending upon the desired number of times of recycling of the product. All obvious combinations of recycling and the use of two or more rolls in any desired arrangement can be employed in the method of this invention.

Both rolls in any given pair of oscillating rolls can be oscillated at the same time or one roll of each pair can be maintained stationary while the other oscillates. The rate of oscillation can vary widely and is generally that which is suflicient to obtain the desired degree of fibrillation and twist set of any given material. The rate of oscillation can be as low as one or two oscillations per minute to as high as 5,000 oscillations per minute, depending upon the throughput desired, the degree of oscillation desired, and the like. Generally, the oscillation rate will be at least oscillations, i.e. movement from one point to another point and then back to that same point again, per minute with rates in the range of from about 1000 to about 4000 oscillations per minute being more feasible with respect to throughput. In general, the faster the oscillation the finer the fibrillated product fibers will be.

The oscillation stroke length will also vary widely, increasing stroke lengths generally giving finer fibrillation product fibers. The stroke length will be any length which will give the desired degree of fibrillation and twist set of any given material but will generally be at least 0.1 inch, preferably from about 0.1 to about 6 inches. The length of the rolls parallel to their axes of rotation, i.e. their longitudinal axes, can vary widely, e.g. from a few inches to several feet, depending upon the width of the twisted product to be fibrillated and number of times that product is to be recycled between the same two rolls.

The spacing of the rolls from one another in any given pair of oscillating rolls will vary widely depending upon the product treated, the degree of fibrillation desired, and the twist set permanency desired. Generally, the rolls will be spaced from one another sufficient to cause rubbing of the rolls on either side of the twisted product treated after that twisted product has been flattened, but insufficient to cause rubbing of the rolls against one another in areas where there is no twisted product therebetween, eg the end portions of the rolls. The force by which the rolls are pushed toward one another can and preferably is made yieldable, for example by use of rubber rolls or by supporting the rolls on air pistons so that the force can be maintained by the rolls on the film but the spacing of the rolls between one another can be varied depending upon the thickness of the twisted product and the extent to which the twisted product is twisted before it passes between the rolls. Generally, the rolls are yieldably forced toward one another to maintain a force on both sides of the twisted product when in a flattened state of at least pounds per square inch of the cross-sectional area of the flattened, twisted product. The maximum force for pressing the oscillating rolls together is limited only by economic considerations such as the rolls rubbing against one another so hard as to cause significant abrasion and wearing of the rolls themselves, and the requirement of undue amounts of energy to even oscillate the rolls over one another much less to fibrillate a twisted film.

The twisted film can be passed between the oscillating rolls at any speed depending upon the results desired. Throughput of twisted products can vary from a few feet per minute up to 1500 to 2000 feet per minute, preferably from about 100 to about 1000 feet per minute. The rolls can be formed from any conventional material such as rubber, metal (steel), plastic, and the like since they operate as conventional rolls and roll in the normal manner while at the same time oscillating parallel to their longitudinal axis. One or both rolls can be idler rolls or one or both rolls can be driven rolls. In the case where one or more of the rolls are driven rolls, the speed at which the roll or rolls is driven can be coordinated to effect the desired withdrawal rate of film from roll 1 of the drawing.

Twisted film to be fibrillated is passed through the oscillating rolls so that the longitudinal axis of the twisted film is substantially perpendicular to the longitudinal axes of the rollers. By substantially perpendicular, what is meant is an acute angle of the longitudinal axis of the twisted film with respect to the longitudinal axis of the oscillating rolls in the range of from 5 to 90".

Generally, any orientable plastic film can be employed in this invention. The film can be uniaxially oriented or in any other multiaxially oriented condition to allow fibrillation thereof. The film can be oriented in any conventional manner including supercooling the film and then orienting same by stretching and the like, or heating the film to a temperature below that at which the film is substantially in the molten state and then stretching same to effect plastic deformation of the film.

Generally, films of polymers containing l-olefins having from 2 to 8 carbon atoms per molecule which have been oriented by stretching in at least one direction so that the film after stretching is at least 3 times longer in the direction of stretching than it was before stretching, ie 3 to 1, can be used. When the film is composed of polyethylene which has a density of at least 0.94 gram per cubic centimeter at C., the ratio of length in the stretched direction to original length should be at least 4 to 1 and when polypropylene is employed this ratio should be at least 6 to 1. Polymers of l-olefins can be made in any conventional manner. A particularly suitable method is that disclosed in US. Patent 2,825,721. The film can be made from the polymers in any conventional manner such as by extrusion, casting, flattening blown tubing, and the like.

Other conventional plastic films that can be employed in this invention include blends and copolymers of 1- olefins as above-described with each other and with other polymers such as polyamides, polyesters, polyvinyl alcohol, acrylic polymers, polyvinyl chloride, polyvinyl acetate, polyvinylidene chloride, and the like. Of course, homopolymers of the l-olefins can be employed as well as the individual polymers mentioned. A stretch or orientation ratio of at least 3 to 1 can also be employed with the films mentioned in this paragraph.

The film can be of any length and width and substantially any thickness, the minimum thickness being that which will produce a substantially self-sustaining film and the maximum thickness being dictated by the capacity of the rolls themselves. Preferably, the thickness of the film will vary from that which is sufficient to form a self sustaining film to about 6 milsv Relatively thick films can be treated by this invention by use of a series of oscillating rolls or by recycling the films through the same oscillating rolls a plurality of times.

In the drawing, roll 1 can be rotated by motor 4 at any desired number of revolutions per minute, the particular revolutions per minute employed in any given process being dependent upon the desired throughput of the system as well as the desired degree of fibrillation and the fibrillating capability of the oscillating rolls employed. Therefore, the rate of rotation of roll 1 will vary widely. However, desired results of the twisting operation are that a twisted film product be obtained which has from about /8 to about 30, preferably from about /2 to about 20, twists per foot of length of the twisted film.

Although not necessary to obtain a permanent set in the twist of the film, it is possible in the process of this invention to heat the film either during or after fibrillation at temperatures elevated above the ambient temperature of the process, preferably from about to about 300 F., in order to increase the degree of permanency of set of the twist. Heating of the film is a strictly optional step and is not necessary to effect the desired results of this invention, these results of fibrillation and twist setting being obtainable without heating when the process of this invention as set forth hereinabove is practiced.

Example Blown tubing formed from a homopolymer of propylene having a melt flow of 3.5 (ASTM D 1238-62T, Condition L) was flattened to form a film 2 mils in thickness and 14 inches wide. The film was molecularly oriented by passing the film through an oven maintained at a temperature of 219 C. at a take-up rate of 450 feet per minute and drawing the heated film so that the stretched length was 14 times greater than the unstretched length. The width of the oriented film was 3% inches.

The film was wound onto a roll and that roll employed in this process and apparatus shown in the drawing.

In the process, motor 4 was operated so a to rotate film roll 1 at 450 rpm. Roll 12 was a drive roll operated so as to pull film from roll 1 at the rate of 50 feet per minute. This rate of withdrawal of the film from roll 1 and the rate of turning of roll 1 produced a twisted film product 8 having nine twists per foot of length. The twisted product also had a diameter of approximately 7 inch.

Roll 10 was a nonoscillating idler roll while roll 9 oscillated at a rate of 1200 oscillations per minute through a stroke of 1 /3 inches. The rolls were originally forced together with a force of about 2 pounds per inch of flattened, twisted film 8 between the rolls per mil of thickness of said flattened, twisted film between the rolls. The twisted film 8 was passed between rolls 9 and 10 seven times (i.e. once originally and six times recycled) before it was wound up on roll 12.

The product wound up on roll 12 was a fibrillated material that resembled twine and had a permanency of twist such that the product tended to remain in the twisted state when in a relaxed state and when not being acted upon by external tensioning, restraining, or twisting forces. The product was very suitable for use as cordage and particularly for use as tying twine and baler twine.

Reasonable variations and modifications are possible within the scope of this disclosure without departing from the spirit and scope thereof.

I claim:

1. A method for forming a twisted fibrillation product without having to separately set the twist in said product comprising twisting a longitudinally, molecularly oriented plastic film about its longitudinal axis, and fibrillating the twisted film by passing same at least once between at least one pair of rolls, at least one roll of said at least one pair of rolls being oscillated in a direction that is both substantially parallel to the longitudinal axes of the rolls in said at least one pair of rolls and substantially perpendicular to the longitudinal axis of said twisted film.

2. The method according to claim 1 wherein said film is composed of at least one of polymers of l-olefins having from 2 to 8 carbon atoms per molecule, polyamides, polyesters, polyvinyl chloride, polyvinyl alcohol, acrylic polymers, polyvinyl acetate, polyvinylidene chloride, and copolymers and blends thereof, and said films are oriented so that their stretched length is at least 3 times the u11- stretched length.

3. The method according to claim 1 wherein said twisted film, before fibrillation, has from about A; to about 30 twists per linear foot.

4. The method according to claim 1 wherein said at least one roll which is oscillated is oscillated at a rate of at least 100 oscillations per minute through a stroke of at least 0.1 inch, and said at least one pair or rolls are yieldably pressed toward one another to maintain a force on both sides of said twisted film being fibrillated of at least 10 pounds per square inch of cross-sectional area of the film passing between said at least one pair of rolls.

5. The method according to claim 1 wherein said film is formed from a homopolymer of propylene, said film is molecularly oriented so that the stretched length is at least 6 times the unstretched length, said at least one pair of rolls are yieldably pressed toward one another to maintain a force on both sides of the twisted film passing therebetween of at least 10 pounds per square inch of crosssectional area of said twisted film passing therebetween, the oscillation rate of said at least one roll is from about to about 5000 oscillations per minute with an oscillation stroke in the range of from about 0.1 to about 6 inches, the film having been oriented so that the oriented length is at least 6 times the unoriented length, and the twisted film before fibrillation has from about to about 20 twists per linear foot.

References Cited UNITED STATES PATENTS 2,185,789 1/1940 Jacqu.

2,545,869 3/1951 Bailey.

2,700,657 1/1955 Look et al.

2,707,805 5/ 1955 Smith et al.

2,930,535 3/1960 Jones et a1.

3,165,563 1/1965 Rasmussen.

3,177,557 4/1965 White 5734 XR 3,199,284 8/1965 Scragg 57157 3,302,501 2/1967 Greene.

FRANK I. COHEN, Primary Examiner.

DONALD E. WATKINS, Assistant Examiner. 

